Automatic spraying techniques have long been employed for painting large articles such as cars, trucks, refrigerators, etc., and small articles, such as vehicle and equipment parts. The items being sprayed are generally advanced along a conveyor line which passes through paint spray booths where a fine spray of paint is automatically directed at the articles being painted from paint spray guns which are located on one side of the conveyor. Oversprayed paint, i.e. paint which does not contact the article being painted, forms a fine mist of paint in the air space surrounding the painted article. This paint mist must be removed from the air. To accomplish this the contaminated air is pulled to the rear of the paint booth by air exhaust fans which are generally located behind the conveyor. A curtain of cascading water is maintained across the path of the air in such a manner that the air must pass through the water curtain to reach the exhaust fans. As the air passes through the water curtain the paint mist is scrubbed from the air and carried to a sump basin, usually located below the paint spray booth (see U.S. Pat. No. 2,585,407). However the water itself does not detackify the paint and unless it is treated to detackify it, it tends to adhere to the sump and drain surfaces. To prevent clogging of the sump drain and sewer system the accumulated paint must be periodically removed from the sump. This is generally accomplished by shovelling, which is costly and time consuming. It is preferable to detackify the paint so that it will not adhere to the surfaces of the waste paint collection system and to cause the detackified paint particles to coalesce for easy removal from the system. It is very desirable to be able to thoroughly separate the waste paint solids from the water so that the water may be recycled and the paint solids properly disposed of.
Various procedures and techniques have been tried to detackify the paint. For instance, U.S. Pat. No. 3,515,575 discloses contacting the paint with inorganic substances, such as clay, starch, colloidal silica, talc, etc., to detackify it. In particular, this patent dislcoses the use of hectorite, a montmorillonite-type clay, for detackifying paints, including oil-based paints, lacquers and enamels. Other U.S. patents which disclose the use of clays to detackify paint are U.S. Pat. Nos. 2,267,426, 4,125,476, 4,185,970, 4,220,456, 4,380,495 and 4,504,395. Although the clay materials described are somewhat effective for detackifying particles of paints which contain pigments and fillers they leave a lot to be desired in the detackification of clear lacquers.
Organic chemical substances such as polymeric flocculants have also been used to detackify paint overspray in spray booths. These systems are superior to the simple use of clays since they facilitate the coalescence and separation of the paint particles from the circulating water system. U.S. Pat. No. 4,002,490 teaches the use of a water-soluble salt of an amphoteric metal, propylene glycol and a polycationic polymer as a paint detackifying composition. U.S. Pat. No. 3,990,986 describes the use of zinc chloride and a polyelectrolyte at pHs above 8 to detackify paint spray booth wastes. This patent also discloses the combination of a metal salt which forms an insoluble hydroxide above pH 7, a primary amino alcohol and a polyether to clarify and detackify paint spray booth wastes. U.S. Pat. No. 4,440,647 discloses the use of a water-dispersible polyamideepichlorohydrin resin, a polymer formed from hexamethylene diamine and ethylene dichloride, and an amphoteric metal salt. This patent also describes the use of ferric chloride in combination with cationic polymers to treat suspended matter comprising water and oil-based paints. U.S. Pat. No. 4,067,806 discloses the use of blends of a terpolymer of dialkyldimethylammonium halide, N-vinyl-2-pyrrolidone and acrylamide and a water-soluble salt of an amphoteric metal, such as aluminum chloride, to reduce the tackiness of over-sprayed paint and lacquer solids in paint spray booths.
The prior art methods of detackifying paint particles is easily applied to pigment-containing latex-based paints and some of these techniques have been applied to pigment-containing and/or filler-containing oil-based paints. In these paints the pigment and/or filler particles serve as a base for agglomerating and detackifying the paint. However, in the case of pigment-free and filler-free oil-based paints, such as clear lacquers, there are no solids to provide a base on which the detackifying agents can act. New solids-free coating materials are being widely used for coatings for automobiles because of the increased protection that they provide to the finish of the automobile. However, these coating materials are more difficult to detackify and remove from spray painting system.